The proposed research will explore the hypothesis that magnetically guided targeting of endothelial cells (EC) to stented arteries can reduce vessel reocclusion (restenosis) following stent angioplasty. Re-endothelialization oriented strategies have potential to prevent restenosis while avoiding the side effects of the currently used therapies. However, in order to fully realize this potential a significant improvement in cell delivery efficiency is required. This study will investigate two novel ideas: 1) the application of magnetic nanoparticles (MNP) for providing EC with magnetic responsiveness adequate for their targeted delivery to stented arteries; and 2) using a uniform field-controlled magnetic targeting of EC to reversibly magnetizable stents for enhanced reendothelialization and inhibition of restenosis post stenting. The present studies will address the following specific aims: AIM 1: MNP characterization with respect to their physical properties, cell compatibility, uptake and degradation kinetics. Biodegradable fluorescent-labeled MNP will be formulated using a modification of the polymer precipitation approach. The size, composition and magnetic properties of MNP will be characterized, and their cell compatibility, internalization and degradation kinetics will be the main endpoints of the Aim 1 experiments. The magnetic responsiveness of MNP and EC treated with MNP will be measured by alternating gradient magnetometer. The kinetic studies will be performed in cultured cells using fluorimetry and global FQrster Resonance Energy Transfer measurements. Cell compatibility of MNP will be determined using fluorimetric cell toxicity assays. AIM 2: EC targeting and reendothelialization studies. Arterial localization and tissue distribution after magnetic vs. non- magnetic delivery of MNP-impregnated EC stably expressing firefly luciferase will be studied by in vivo bioluminescence and luminometry, respectively, in the rat carotid stenting model. The local kinetic profiles of stent-targeted cells will be compared 1, 7 and 28 days post treatment with endothelialization determined using a quantitative immunohistochemical strategy. AIM 3: antirestenotic efficacy of targeted EC. The extent of restenosis in animals treated under magnetic conditions with MNP-loaded EC will be determined by computerized morphometry and compared that in non-magnetic delivery and 'stenting only' controls four weeks post delivery.